The First World War introduced new tasks into British policing. One significant addition was the close and systematic surveillance of aliens residing in Britain, a role never before undertaken by the British police and one that would previously have been considered un-English. During the war, various official bodies participated in the regulation of the lives of foreigners, but the police played a crucial part. Foreigners hailing from enemy countries, particularly Germans, bore the brunt of police attention, which can be described as nothing short of discriminatory and oppressive. This article examines the new responsibilities of the British police for controlling German nationals and the public response to the new policing. It also assesses the police's wartime performance and the implications of their conduct for the lives of these Germans, all of which has hitherto been little explored. The police were widely considered, both by large segments of the British public and in many other countries, as the best police force in the world, morally superior to other constabularies, especially in their relatively tolerant attitudes toward the public. Their conduct in a time of national crisis, and particularly the degree of tolerance they exercised in their relations with a hated, indeed outcast minority, offers an illuminating case study.